Symmetry breaking by proton-neutron pairing

The symmetries of the t = 1 and t = 0 pair-fields are different. The conseq uences for rotational spectra are discussed. For t = 1, the concept of spon taneous breaking and subsequent restoration of the isospin symmetry turns o ut to be important. It permits us to describe the proton-neutron pair-corre lation within the conventional frame of pairing between like particles. The experimental data are consistent with the presence of a t = 1 field at low spin in N approximate to Z nuclei. For a substantial t = 0 held, the spect ra of even-even and odd-odd N approximate to Z nuclei become similar. The p ossibility of a rotationally induced J = 1 pair-field at high spin is consi dered.